Eleven patients with effort angina and a history of cold intolerance performed short-term bicycle exercise tests at various room temperatures, 20, 10, 0 and -10 degrees C, and a few patients also at -30 degrees C. A significant reduction of maximal working capability (expressed as maximal work load, MWL), limited by moderately severe angina, was found at -10 degrees C (7% +/- 1, SEM, P less than 0.05) compared with normal room temperature. At 0 and 10 degrees C changes of MWL were small and not significant, and at -30 degrees C no further decrease of MWL was seen. About half of the patients, however, showed a tendency toward a decrease in MWL with decreasing environmental temperature, and and the decrease in MWL correlated significantly with an increase in rate pressure product (RPP) during exercise at both 0 and -10 degrees C. Thus, the decrease in working capability on exposure to cold could be explained by an increase in heart work. Warming up effects of exercise, counteracting the cold-induced increase in peripheral vascular resistance, were indicated by a diminishing difference in systolic blood pressure between a cold and normal environment with increasing work time.